For example, Japanese Patent Application Publication No. 4-346295 describes a fixing structure of a flexible circuit board to a cooler, such as a heat sink. Multiple electronic parts are fixed to the circuit board, and the circuit board is fixed to the heat sink in a winding manner.
The circuit board is made of a flexible resin film or a resin film backed with metal or the like. The circuit board has a single or multi layer structure of electrodes and wiring layers. The electronic parts are discrete parts including resistors and IC parts such as LSI chips. The electronic parts are fixed at a first surface of the circuit board to form a desired electronic circuit with the wiring layer. The circuit board to which the electronic parts are fixed is mounted to projections of the heat sink in a state where portions between the electronic parts are bent. In this case, back surfaces of the electronic parts are in pressed contact with side surfaces of the projections by a pressing force caused by bending the circuit board, thereby to improve cooling efficiency.
In such a structure, however, only the back surfaces of the electronic parts are closely in contact with the heat sink.
In order to further improve the cooling efficiency, it may be considered to make the circuit board to contact with the heat sink so that the electronic parts are cooled from both sides. In such a case, a front surface of the electronic parts may be fixed to the projection through the circuit board. In the structure of Publication No. 4-346295, however, there is a clearance, such as an air space, between the first surface of the electronic part and the circuit board. That is, because a clearance remains between the heat sink and the electronic part, it is difficult to further improve the cooling efficiency.
Further, engagement portions need to be formed on surfaces of the projections of the heat sink and the circuit board to ease positioning of the electronic parts relative to the heat sink and restrict displacement of the electronic parts after the mounting. For example, engagement projections are formed on the surfaces of the projections of the heat sink, and engagement holes are formed on the circuit board to be engaged with the engagement projections. Alternatively, a recess or a projection corresponding to the outer shape of the electronic part needs to be formed on the surface of the projection, and the electronic part is engaged with the recess or projection.